This invention relates generally to a method for preparing organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals. More specifically, the method involves the reaction of aminoalkylsilanes and siloxanes with acyl halides in nonaqueous media and in the presence of metal alkoxides to produce acylamino organosilicon compounds.
Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in U.S. Pat. No. 4,608,270 to Varaprath which is herein incorporated by reference.
As mentioned in Varaprath U.S. Pat. No. 4,608,270 and as taught in U.S. Pat. No. 2,929,829 to Morehouse, Japan No. 51/08022 to Furuya et al, Japan No. 56/74113 to Takamizawa and West German No. DE 2365272 to Koetzsch et al., acylaminoorganopolysiloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However, such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer especially when the acid chloride has other reactive vinyl functionality such as where the acid chloride is acrylyl chloride.
An alternative method for the preparation for the acylamino organosilicon compounds involves the reaction of aminosiloxanes and silanes with an acid anhydride or ester at elevated temperature. This is taught in U.S. Pat. No. 4,507,455 to Tangney and Ziemelis, assigned to the assignee of the present invention. Unfortunately at the elevated temperatures of the reaction, arcylamide derivatives undergo Michael addition and amidation of the acrylic double bond resulting in unwanted byproducts and crosslinkage of the desired product which ultimately causes the polymer to gel.
Finally as taught in the above mentioned U.S. Pat. No. 4,608,270 to Varaprath, also assigned to the assignee of the present invention, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of aqueous sodium hydroxide. However, a problem arises from the fact that this reaction is carried out in a two-phase system in which the aminosiloxane is dissolved in an organic solvent that is immiscible with water. The HCl that is produced on addition of acyl chloride is neutralized by hydroxide in the aqueous phase. Because the amide function is generally highly polar and hydrophilic, it shows a great tendency to absorb moisture. Incorporation of these units into the siloxane backbone increases water miscibility causing the polymers to emulsify easily thus making phase separation difficult. To some extent, this problem can be overcome by using chlorinated solvents such as methylene chloride or chloroform but, unfortunately, such solvents are toxic. Moreover, when larger amounts of amide functionality or more resinous structure or both are used, it becomes very difficult to prepare such compounds using a two-phase system even when chlorinated solvents are used. Finally, because of the presence of the aqueous phase, it is impossible to prepare aminosilanes containing hydrolytically unstable groups using this process.
Accordingly, the need remains for an improved method for preparing acylamino organosilicon compounds which avoids the phase separation and toxicity problems previously encountered. The need also remains for an expanded method which permits use of silane starting materials having hydrolytically unstable groups such as CH.sub.3 OSi.